Abstract: Coal seam gas pressure is an important parameter to predict coal and gas outburst, so fast and accurate manometry of coal seam is very important. But mang failed phenomenon occured in practice of Ｍ-Ⅱ gas pressure determinitor. As a result, we firstly analyzes the influence factors leading to failed fast manometry according to the measuring principle and procedure, and then proposes the corresponding measures to ensure the sucess of fast manometry of coal mine.